Abstract: Based on data analyses of seismic, well drilling, logging, and stratigraphic correlation and thickness, we conduct an in-depth
investigation of the slope break belt in the Quantou Formation, Gulong sag, Songliao Basin. Results show that there are three types of
belts in the study area, i.e., fault slope-break belt, flexural slope-break belt and depositional slope-break belt. The slope-break belts
distribute in a north-south arc pattern along the Yingtai nose-shape structure of the west of the Gulong sag. Average gradient of the belt
ranges from 19‰ to 50‰ . The development of the slope break belt controls the structures of sedimentary sequence and the
sedimentary environment. The fault slope break belt develops at the bottom of the sequence, and controls the development of the SQ11
aggradation sequences of fluvial facies. It is characterized by that the thickness of the lower sequence is 2 times that of the upper
sequence. The flexural slope-break belt develops in the middle of the sequence, and presents a two-section feature of the gentle slope
belt (α) and the steep slope belt (β). The fourth order sequence SQ21 developed dense onlap points in the slope belt, forming a
lacustrine onlap sequence structure. The thickness of the strata in the two sides of the slope belt is characterized by thinner upper part
and thicker lower part. The depositional slope-break belt distributes on the top of the sequence, which controls the development of the
fifth order sequence SQ22-1, forming a progradation sequence of laucustrine delta facies. Its thickness is characterized by thinner lower
part and thicker upper part. The fault slope-break belt controls the aggradation sequence of fluvial facies, which is beneficial for the
development of traps with upward-dip sheltering by fault and point-bar lens. The flexural slope-break belt controls the lacustrine onlap
sequence, which is beneficial for the development of lithologic traps that are characterized by the styles of updip wedge-out. The
depositional slope-break belt controls the progradation sequence of lacustrine delta facies, which is beneficial for the development of
the mouth bar lithologic traps. Therefore, the study of the slope-break belt is of significance to the oil and gas exploration in the Gulong
sag of the Songliao Basin.

Key words: Songliao Basin , Gulong Sag, slope break belt, sequnce and sedimentation